]872.] Sir B. C. Brodie on the Action of Electricity on Gases. 473 



desired to estimate the changes in volume produced by the experiment, was 

 the principle of pipette-measurement which has been so successfully em- 

 ployed by chemists for the measurement of liquids. In this way a con- 

 siderable volume (say from 250 to 300 cub. centims.) may be measured with 

 facility and precision. A definite volume of gas was thus always operated upon. 



The gas having been measured in the pipette was drawn over by means 

 of a mercurial aspirator, an instrument which served the double purpose of 

 an aspirator and measurimg-apparatus. The principle of this aspirator was 

 that originally employed in the apparatus of Regnault for measuring the 

 volumes of gases, namely, the estimation of the pressure and temperature 

 at which the gas occupied a known space, from which the volume of the 

 gas at standard temperature and pressure was calculated. By means of 

 this apparatus a change in the volume of the electrized gas, to the extent of 

 about 1 part in 1000, could be accurately estimated; that is to say, after 

 the calibration of the apparatus, 1000 volumes of gas as measured in the 

 pipette were found to measure 1000*7 volumes in the aspirator. These 

 numbers represent the errors of the experiment, and any differences in the 

 volume of the gas beyond this limit must be considered to be due to the 

 experiment to which the gas was submitted. The pipette and the aspirator 

 were placed on a table, separated by an interval of about 8 or 10 inches. 



In Section II. the results are given of passing the electrized gas through 

 a solution of neutral iodide of potassium, also of heating the gas, of passing 

 the gas over metallic silver, copper, gold, aluminium, and binoxide of man- 

 ganese, and of the decomposition of a solution of binoxide of sodium effected 

 by the passage of the gas, a quantitative estimation of the changes in 

 the volume of the gas and the oxidation effected being in all cases made. 



The precision attained in such experiments may be estimated by the re- 

 sults of the measurement of the gas before and after its passage through a 

 solution of neutral iodide of potassium. As the mean of eight concordant 

 experiments, 100 cub. centims. of gas, as measured in the pipette, were found 

 after the experiment to measure 99*93 cub. centims. in the aspirator. An 

 oxidation was effected in the solution of neutral iodide of potassium equivalent 

 to 3*77 cub. centims. of oxygen ; that is to say, 3*77 cub. centims. of oxygen 

 were thus removed from the gas without an appreciable variation in its vo- 

 lume. The volume of the gas thus absorbed by neutral iodide of potassium 

 was in subsequent experiments assumed as the unit to which other analo- 

 gous variations were referred. 



When the electrized gas is passed through a solution of binoxide of 

 sodium, an increment occurs in the volume of the gas. Thus in two experi- 

 ments the increment in the volume of the gas, as estimated from the 

 difference of the volumes in the pipette and the aspirator, was 1*93, 1*99, 

 the "titre" of the gas (as just explained) being taken as 1 ; and the ratio 

 of the sum of the oxygen lost by the binoxide of sodium (as estimated by 

 titration of the solution of binoxide of sodium before and after the experi- 

 ment with permanganic acid) and the titre of the gas to the titre of the gas 



